#include <iostream>
#include <cmath>

// 用函数模板求解定积分
class F1
{
public:
    double fun(double x) { return x * x; }
};
class F2
{
public:
    double fun(double x) { return x; }
};

template <typename T>
class Integrate
{
    double a, b;
    int n;
    T cf; // 传递被积函数
public:
    Integrate(double _a, double _b, int _n = 10000) : a{_a}, b{_b}, n{_n} {}
    double integrate()
    {
        double result{(cf.fun(a) + cf.fun(b)) / 2};
        double h{(b - a) / n};
        for (int i{1}; i < n; i++)
            result += cf.fun(a + i * h);
        result *= h;
        return result;
    }
};

int main()
{
    Integrate<F1> i1{0, 1};
    Integrate<F2> i2{0, 1};
    std::cout << i1.integrate() << '\n'
              << i2.integrate();
}